A PON is a system for providing network access over a final portion of a telecommunications network. A PON is a P2MP network comprising an OLT at a CO, an ODN, and ONUs at user premises. PONs may also comprise RNs located between the OLTs and the ONUs, for instance, at an end of a road where multiple customers reside.
In recent years, TDM PONs such as GPONs and EPONs have been deployed worldwide for multimedia applications. In TDM PONs, the total capacity is shared among multiple users using a TDMA scheme, and as a result the average bandwidth for each user may be below 100 Mb/s. EPONs use WDM and provide rates up to 10 Gb/s. Next-generation EPONs may be required to implement 100 Gb/s due to increasing customer demands.
Future approaches include four-channel WDM networks with 25 Gb/s bit rates per wavelength channel and fewer-channel WDM networks with even higher bit rates per single channel. As bit rate demand continues to increase, bandwidth restrictions meant to efficiently use existing devices may result in severe ISI. ISI is a significant challenge for CDR for high-speed PONs. In particular, for high-speed, upstream, burst-mode transmissions in PONs, a converging speed and a quality of the CDR can significantly affect data transmission quality.